Underlay & vertical battens required?

Guest User
8/30/2008
I am considering an interlocking, stone coated metal shake-style shingle installed on horizontal 2x2 battens over our 14 yr old asphalt shingle roof with a 4/12 slope. The installer maintains (a) that NO underlay over the asphalt shingles is required, and (b) that vertical battens are NOT required in addition to the horizontal. His reasoning is (a) that the interlocking nature of the metal panels creates a leak-proof surface rendering an underlay unnecessary, and (b) the shingle is so designed as to create a vertical airflow sufficient to dry any condensation that may occur on the underside of the panel, without the need for vertical battens. Your advice?
Todd Miller
Isaiah Industries, Inc.
8/30/2008
I am not 100% certain but I believe that the manufacturer of his product would agree. However, do check with them. Just the same, I always think underlayment is wise and etchnically I feel it is required by code and also by industry guidelines. As far as vertical battens ... they could help with the energy efficiency of your roof system.
Guest User
8/31/2008
A followup question: if only horizontal battens are used, wouldn't they prevent the downward flow of any water on the underlayment? Since the underlayment is not designed to retain standing water, is there any point to using it without also using vertical battens? Without vertical battens, it seems the underlay would, at best, slow down the rate of any water penetration, should a leak occur.
Todd Miller
Isaiah Industries, Inc.
8/31/2008
Generally, if the panels are installed properly, there should not be much moisture underneath the panels ever. The airgap will allow evaporation of any condensation. The horizontal battens are installed with a gap between them and I have also seen one manufacturer of stone coated steel suggest the use of battens that have slots milled into the bottom of them. Again, I cannot stress enough how critical it is to get the recommendation of your roofing manufacturer and follow it.
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